1. Deron Williams
The story of Deron Williams is the most shocking and horrific act of betrayal that any former Jazz player has ever inflicted on the squad. His attitude and ego led him to a campaign of tyranny that saw him directly butt heads with Jazz icon Jerry Sloan. Sloan is easily the most likable and respected ex-Jazz 'anything' (player/owner/coach, etc) the franchise has ever had. He's among the most respected men to ever coach or play in the NBA. He demanded a work ethic out of his squad that led him to 20+ years of success in Salt Lake.
Then Williams came around. He started getting too big for his britches and started believing that he was being held back. This led to so many fights between him and Sloan that the relationship went sour and then imploded. The hatred the two men felt for one another was so bad that when it was all said and done, the team lost both men.
Williams demanded a trade, and was granted his request ending up in New Jersey with the Nets, and then with Sloan retiring mid-season, having had enough of the nonsense. Many people, rightfully so, blamed Williams for pushing Sloan to retirement, something he's taken some responsibility for over the years.
While Williams on the court was easily the number one biggest turncoat in franchise history, he's since done everything he could to make amends with the franchise, even healing his relationship with Sloan before Sloan's passing. Williams is now welcomed back to Salt Lake City to be celebrated as the franchise legend that he is, but during his playing days, he was enemy number one in Utah.